The present invention relates to supercritical fluid chromatography and, more particularly, to an apparatus for analyzing a process stream via supercritical fluid chromatography having improved pump means for drawing a substance from a container means and delivering a pressurized substance to the analyzing system.
Supercritical fluid chromatography is an analytical technology which permits the analysis of high molecular weight samples in a rapid and efficient manner. The supercritical state is the region above a substance's critical point, which is defined as the temperature and pressure at which the liquid and vapor phases of the substance exists in equilibrium with each other and become identical, forming a single phase. Above this critical point in temperature and pressure, the fluid has a viscosity close to that of a gas but the solubility of a liquid and therefore is uniquely suitable as a mobile phase for transporting a high molecular weight compound through very small diameter tubes and conduits in an analyzer such as a chromatograph. There are several substances which are well known as potential supercritical fluid phases including ammonia, pentane, isobutane, and carbon dioxide.
A supercritical fluid is commonly obtained by pressurizing and heating a substance above its critical temperature and pressure. Once in this supercritical state, a substance will not become a liquid no matter how much pressure is applied. It is necessary to provide pumping means for the pressure to convert a substance to a supercritical fluid. Heretofore, such pumping means have been complicated and cumbersome and have restricted the use of supercritical fluid chromatography in on-line process analysis.